It is well known that vinyl resins may be plasticized or changed from the hard, horny and stiff state to a soft, plastic workable condition by the addition thereto at elevated temperatures of certain plasticizers, such as dioctyl phthalate, and the like. These vinyl polymers or resins are referred to as dispersion resins or paste resins and are usually made employing an emulsion polymerization technique, although in some instances, a suspension polymerization process can be used.
When the vinyl resin is mixed or blended with a plasticizer, it is referred to as a "plastisol". By virtue of the flowability of the plastisol it can be processed into various useful products. The plastisols can be used in making molded products, coatings, and the like. Accordingly, the dispersion or paste resin must be capable of being mixed with a plasticizer easily and uniformly to form low viscosity plastisols which are stable, containing particles of uniform and proper size, and capable of producing films, and like products of good clarity.
With the customary emulsion polymerization process, suitable latices have been difficult to obtain since the latices usually contain particles of varying size and are either too fine or too large.
Various proposals have been made to overcome these difficulties but not with the ultimate success desired. For example, the use of various different emulsifiers and catalysts have been proposed. Also, varying the conditions of polymerization has been suggested. However, in most of these cases, partially agglomerated particles have resulted which precipitate reducing the yield of desired polymer. Further, the shelf-life of such latices leave much to be desired. It is desirable to have latices which change very little during storage with respect to viscosity and have and maintain good heat stability.
In U.S. Pat. No. 4,076,920, issued Feb. 28, 1978, wherein a special emulsification system and polymerization conditions are employed, a very desirable dispersion resin is produced which overcomes most all of the problems spelled out above. However, there is another detrimental problem in the commercial production of polymers and copolymers of vinyl and vinylidene halides, when polymerized alone or with other vinylidene monomers having a terminal CH.sub.2 .dbd.C&lt; group, namely the formation of undesirable polymer buildup on the inner surfaces of the reactor. This deposit or buildup of polymer on the inner surfaces of the reactor not only interferes with heat transfer, but also decreases productivity and adversely affects polymer quality, such as producing fiber particles than desired with the resultant adverse effect on viscosity. Obviously this polymer buildup must be removed after each charge or cycle since more buildup occurs rapidly on that already present resulting in a hard, insoluble crust. It is desirable to be able to polymerize a plurality of charges before having to shut down for cleaning purposes. Prevention of the formation of the buildup would be the ideal. Therefore, there is a definite need in the art for a polymerization process which meets all of these criteria discussed above.